ANTIBODY MAPPING TO DOMAINS OF BOTULINUM NEUROTOXIN SEROTYPE-A IN THECOMPLEXED AND UNCOMPLEXED FORMS

The domain organization of the botulinum neurotoxin serotype A was stu died by using antibody mapping of 44 monoclonal single-chain variable fragments, The analysis was carried out on (i) the individual domains of botulinum neurotoxin holotoxin (binding, translocation, and catalyt ic), (ii) botulinum neurotoxin holotoxin, (iii) the botulinum neurotox in holotoxin in complex with the nontoxic portion, and (iv) botulinum neurotoxin holotoxin and nontoxic portion of the complex recombined in vitro. All 44 antibodies mapped to individual domains of botulinum ne urotoxin. Forty of the 44 single-chain variable fragments bound the bo tulinum neurotoxin holotoxin relative to the isolated domains, suggest ing that 4 epitopes are covered when the individual domains are in the holotoxin form. Only 20 of the antibodies showed a positive reaction to the toxin while in complex with the nontoxic portion. All of the co vered epitopes were mapped to the binding domain of botulinum neurotox in, which suggested that the binding domain is in direct contact with the nontoxic portion in the complex, Based on the antibody mapping to the different domains of the botulinum neurotoxin holotoxin and the en tire complex, a model of the botulinum neurotoxin complex is proposed.